Drawbars are used in integral or unit trains to permanently connect rail cars together. The drawbars replace the conventional E and F couplers used heretofore to detachably couple the cars. Preferably the drawbar connections are made slackless, as by gravity wedges, so as to minimize impact forces.
Drawbars are used in transporting unit trains for bulk commodities, such as ore, taconite, coal, grain, phosphate and the like. Rotary drawbars permit commodities to be discharged or emptied by rotating each car individually while still permanently connected to an adjacent car. The connecting structure is incorporated in the cars as a slackless drawbar having a rotary connection at one end of one car and a fixed or non-rotatable connection at the opposite end. However, where the rotary slackless connection includes a gravity wedge, car rotation may displace the wedge.
As explained above, the loaded cars of the trains may be individually rotated and emptied at an unloading or discharge station. In the unloading procedure, the cars are spotted or located at the entrance to the discharge station. To this end there is provided an on site car indexer or positioner system which serves to move the train and sequentially spot or individually index each car into the discharge station.
The car positioner system includes a power driven carriage which travels on a runway parallel and adjacent to the railway track on which the unit train to be unloaded is located. A pusher arm is mounted on the carriage and is movable to a position for engagement with the car coupling devices located between the cars for moving the cars into a discharge station.
Pusher arm heads on the positioner systems currently in use are designed for use with railcars interconnected with articulated couplers by either engaging both coupler heads at the coupled connection or engaging a striker casting fixed to the end of the center sill of one car from which a coupler extends.
In one type the pusher arm head is designed to embrace or encompass the coupled heads about the knuckle and guard arm sides of E or F couplers to move the railway cars. Another design utilizes the pusher arm head to interengage between the striker casting and the E or F coupler heads extending therefrom to move and position the car into the dumping or unloading station.
Both of these pusher arm designs require structural features peculiar to the E and F coupler heads which features normally are not present on the shank of a drawbar. Moreover striker castings are not required when a drawbar connects two railcars and recent railway car design for drawbar connection has eliminated the striker casting to reduce the car weight.
The slackless rotary dump drawbar structure as heretofore mentioned may be permanently connected between railway cars. Examples of slackless drawbar systems, including car connections, are illustrated in U.S. Pat. No. 4,456,133. As shown and described the slackless drawbar system is constructed in a manner to provide zero slack to eliminate impact forces which occur during run-in and run-out of slack. Essentially the slackless construction includes a wedge located so as to drop by gravity to occupy the space caused by any longitudinal wear which may occur at the connected ends of the drawbar. Ultimately, the wedge, drawbar and associated component surfaces may wear to such an extent such that the wedge does not take up the slack and the connections must be adjusted to regain the slackless relationship.